Floating platform



May 1, 1962 WA NESBITT FLOATING PLATFORM 6 Sheets-Sheet 1 Filed April50, 1957 INVENTOR W1 LL MM A, A/iia/rr BY WWW May 1, 1962 w. A. NESBlTTFLOATING PLATFORM 6 Sheets-Sheet 2 Filed April 30, 1957 INVENTOR.WILLIAM A, A/iia/rr ATTOPA/EYS May 1, 1962 w. A. NESBITT 3,031,997

FLOATING PLATFORM Filed April 30, 1957 6 Sheets-Sheet 3 I WW9 I62 v fx/i/ INVENTOR.

May 1, 1962 w. A. NESBITT FLOATING PLATFORM 6 Sheets-Sheet 4 Filed April30, 1957 May 1, 1962 w. A. NESBITT FLOATING PLATFORM 6 Sheets-Sheet 5Filed April 30, 1957 I l INVENTOR.

W/mM 4, Mam/r1 United States Patent Of" 3,031,997 FLOATING PLATFORMWilliam A. Nesbitt, 4315 Myrtle Ave., Long Beach, Calif. Filed Apr. 30,1957, Ser. No. 656,035 9 Claims. (Cl. 114.5)

This invention relates to a floating platform and an anchorage systemtherefor, and has for its main object the provision of compensation forthe platform such that the platform is maintained at a constantelevation above the bottom of the sea and at a constant level positionin spite of changes in deck loading and the effects of tide, waves, Windand under-Water currents acting on the platform. More specifically, theinvention relates to such a platform as is usable in off-shore drillingoperations, either as a platform usable directly for well drilling, oras a means for the erection of a permanent drilling platform in deepwater.

Many valuable pools of oil have been discovered in the tidewater areasof the United States, and many offshore drilling operations have beencarried out to pro duce this oil. However, the present operations havebeen restricted to areas in which the water has been relatively shallow,such that pilings or towers could be erected which would support thedrilling apparatus directly on the sea floor. As yet, it has not beenpractical to carry out drilling operations in deep water, because of theinability to provide a constantly level drilling platform at a fixedheight above the sea floor. As is obvious, for any drilling to becarried out in deep water, the drilling apparatus must be fixed at anelevation above water level, and must not be subjected to changes in itslevel position. In such a drilling operation, the drill pipe is fixedwith respect to the sea floor, and is also fixed with respect to thedrilling platform. If the platform is free to rise and fall with tideand waves, an undue strain will be placed on the well string, whichwould cause it to pull apart. If the platform were to be tilted, as fromwind or sea currents, a flexing force would be applied to the wellstring which would also cause a rupture of the well string. Similarly,if the well string was being launched from the platform, a tilting ofthe platform would result in a tilting of the well string such that thewell would not be produced from the point desired.

There have been attempts to produce a platform which would overcome thetide and wave actions by providing submersible pontoons spaced below theplatform so that the pontoons could be submerged below the lowest waterlevel to be encountered, with the pontoons being anchored to the bottomof the sea. Such systems have the disadvantage that the platform canonly be loaded to the amount of buoyancy acting upwardly on theplatform. If the buoyancy factor is relatively large so as to enablefairly large loads to be taken aboard, very heavy anchors and anchorcable must be provided to withstand the buoyancy of the system when theplatform is unloaded. If the initial buoyancy is small, enabling lighteranchors and anchor cables to be used, then the amount of loading whichthe platform can handle is diminished. Furthermore, the changes inbuoyancy of the system will vary as the loading varies, thus producingchanges in anchor cable tension and thus varying the length of thecables. It is a feature of the present invention that such a platformcan be loaded between wide limits, without affecting the tension in theanchor cables, thus enabling the system to be more stable.

Another, and more serious, drawback of the devices which have beenproposed is that there has been no compensation for the tilting effectof a sidewards force on the platform, as from tidewater currents orwind. Any submerged platform system, anchored by cables to the seafloor, will present a system in which a sidewards 3,031,997 Patented May1, 1962 force will tilt the platform. It is another feature of thepresent invention that automatic means are provided to vary theindividual buoyancy of the submerged pontoons in such a manner, as willbe explained, as to overcome the tendency of an applied sidewards forceto tilt the platform.

It is an object of the present invention to provide a floating platformhaving submergible pontoons, or buoyancy tanks, anchored by cables to asea floor with means responsive to vertical loading of the platform toadjust the buoyancy of the buoyancy tanks to compensate for changes inthe vertical loading of the platform.

It is a further object of the invention to provide a floating platformhaving submerged buoyancy tanks anchored by cable to a sea floor, withmeans responsive to horizontal loading of the platform for adjusting thebuoyancy of the buoyancy tanks to compensate for said changes inhorizontal loading to prevent tilting of the platform.

It is a yet further object to provide a floating platform havingsubmerged buoyancy tanks anchored by cables to a sea floor with meansresponsive to variations in vertical loading of the platform to maintaina constant total tension in the cables, and with means responsive tovariations in horizontal loading of the platform for adjusting thebuoyancy of the buoyancy tanks to prevent tilting of the platform.

Other objects and advantages will be apparent in the course of thefollowing detailed description.

In the drawings, forming a part of this application, and in which likereference numerals are used to designate like parts throughout the same,

FIG. 1 is an elevational view of the platform and mooring meanstherefor.

FIG. 2 is an enlarged view of the platform and mooring means.

FIG. 3 is a plan view on an enlarged scale of the platform of FIG. 1.

FIG. 4 is a plan view of the platform and mooring means shown in FIG. 1.

FIG. 5 is a fragmental view illustrating a tension responsive means forindicating the total cable tension of the mooring means.

FIG. 6 is a fragmental view illustrating a level responsive means usablefor indicating the levelness of the platform.

FIG. 7 is a wiring diagram illustrating the manner in which thereversible pumps in the buoyancy tanks of the platform are controlled bythe tension responsive and level responsive means of FIGS. 5 and 6.

FIG. 8 is a series of schematic figures and force diagrams illustratingthe operation of the invention.

In the drawings, wherein for purposes of illustration is shown apreferred embodiment of the invention, the reference numeral 10 refersgenerally to the platform structure, which comprises an upper deck 11and lower deck 12, each being generally H-shaped in surface area, andspaced apart to form rooms or compartments 13 therebetween. These roomsare used as living quarters, machine shops, generator rooms, storagerooms and the like.

A drilling derrick 14 is provided on the upper deck, generally centrallythereof, along with crane booms 16 and 17, the latter being usable forloading and unloading barges, such as 18', which may be brought withinthe bays 21 and 22 formed by the H-shape of the platform 10.

Secured to and spaced beneath the platform 10 are a plurality ofpontoons, or buoyancy tanks, 23, 24, 25 and 26, one of each being spacedbelow one corner of the platform structure by suitable framing structure27. Each of the framing structures has at least one hollow pipe, as at28, communicating the interior of the pontoon to which it is connectedwith atmosphere, to provide a vent for that pontoon. Each pontoon 23,24, 25 and 26 has disposed therewithin a reversible motor-pump, 29, 30,31 and 32, respectively, adapted to pump water into, or out of eachpontoon, so that the buoyancy of the pontoons may be individuallyadjusted, in a manner to be hereinafter described.

A plurality of anchor elements 33 are disposed on the floor 34 of theocean, in a pattern corresponding generally to the number and spacing ofthe pontoons 23, 24, 25 and 26, to provide a bottom anchorage for anchorcables 36 to 43, inclusive. As best seen in FIGS. 2, 3 and 4, cables 36and 37 are both connected at their lower ends to a single anchorelement, with cable 36 extending upwardly therefrom, passing upwardlyaround pulley 44 mounted on the lower edge of pontoon 23, and passingaround pulley 46 to the capstan 47 to be secured thereto in aconventional manner. The other cable 37 passes around the pontoon 24 ina similar manner and is secured to capstan 48. Similarly, each of theother groups of cables 3839, 4041 and 4243 extend from a differentanchor element upwardly around the pontoons on the sides thereof facingthe vertical axis of the platform, with one cable of each group beingsecured to a different capstan; i.e., cables 36, 38, 40 and 42 aresecured to capstan 47 and cables 37, 39, 41 and 43 are secured tocapstan 48. The cables on the two capstans 47 and 48 are wound aroundthe capstans in opposite directions to balance the torque action of thecables on the platform.

The capstans are adapted to be rotated by a common drive means,indicated on FIG. 2 as a motor 50, having a drive shaft 51 connected todriving gear 52 in mesh with gear 53 which has capstan 48 rigidly fixedin a coaxial relation thereto. Idler gears 54 and 55, fixedly mounted onshafts 56 and 57 rotatably journaled in platform 10, transmit therotative movement of gear 53 to gear 58 on which capstan 47 is rigidlyfixed in a coaxial relation, so that capstan 47 turns in an equal amountand opposite direction to capstan 48. Gears 53 and 58 are spaced apartto provide an opening directly beneath derrick 14 so that unobstructeddrilling operations may be carried out. It is to be realized that theparticular gearing shown whereby capstans 47 and 48 are rotated is notcritical, as other forms of drive to accomplish this function may beused, if desired.

By the operation of motor 50, the capstans 47 and 48 may be rotated topull the pontoons 23-26 downwardly under the surface of the water to adesired position. At such a position, the pontoons 23-26 will be belowtheir normal flotation level and will exert an upward pull on the anchorcables 36-43.

It is important in the operation of the invention that means he providedto indicate a change in the total tension of the anchor cables. Oneexample of such means, illustrated generally in FIG. by the referencenumeral 60, is a device wherein a brake lever 61 is provided which isadapted to be rigidly secured by conventional means to idler gear shaft56 after the platform pontoons have been submerged to a desired level.The total cable tension will be exerted on shaft 56, which is thenprevented from rotating under this tension by the braking action oflever 61- on piston 62. of the oil filled reservoir 63. The reservoir 63is fixedly secured to platform 10. The pressure on the oil in thereservoir exerted by the brake lever 61 is transmitted into cylinder 64to act on one side of piston 65 reciprocable therein. Compression spring66 on the other side of piston 65 balances the force exerted by the oilon the piston, and rod 67 transmits the reciprocable movement of piston65 to the movable switch arm 68 of switch 69. If the total cable tensionincreases, the brake force on piston 62 will increase, causing the oilto flow into cylinder 64 to move the piston 65 leftwardly against thebias of spring 66 and thus to move switch arm 68 to the left. If thetotal cable tension decreases, the brake pressure on piston 62 willdecrease, and spring 66 will move piston 65 to the right, causing switcharm 68 to move to the right.

The spring 66 abuts adjustment member 71 which is threadedly secured tocylinder 64 and is longitudinally adjustable relative thereto so thatthe spring bias of spring 66 may be varied as desired, in order toadjust the mechanism so that switch element 68 will be in the neutral oroff position for any desired amount of total cable tension.

Again, it is to be understood that the particular form of means toindicate the change in total cable tension herein illustrated isintended merely as an example of one such device, and that other devicescapable of indicating tension and changes thereof may be used in thepresent invention.

It is also important in the practice of the invention to provide aplurality of level indicating means which will be responsive to atilting of the platform. A simple form of such an indicating means isthat illustrated in FIG. 6, wherein a closed ring tube 73 ofelectrically non-conductive material is suitably mounted on a portion ofplatform 10, with the legs 74 and 75 of the tube extending in agenerally vertical direction. The tube 73 is filled with mercury suchthat when the platform 10 is in a level position, the mercury will be atlevels 76 and 77, respectively, in legs 74 and 75. A first contactelement is positioned in leg 74 slightly above the normal height of themercury level 76 therein, and a second contact element 79 is positionedin leg 75 slightly above the normal height of the mercury level 77therein. A third contact element is positioned in the lower part of ringtube 73 so as to be in contact with the mercury at all times. Theoperation of the leveling means is quite simple. If the platform 10should tilt such that the left side of the platform should be lower thanthe right side, as viewed in FIG. 6, the contact 78 will be immersed inthe mercury to complete a circuit between contacts 78 and 80. Similarly,if the platform tilts in the opposite direction, a circuit will becompleted between contacts 79 and 80. If the platform 10 is level, bothcontacts 78 and 79 will be above the mercury level and no circuit willbe complete through the device.

The level indicating means illustrated in FIG. 6 are disposed, one ineach corner of the platform, as in the dotted positions 81, 82, 83 and84, and are arranged such that the vertical legs 74 and 75 thereof aregenerally in the vertical plane defined by the vertical axis of theplatform and the respective pontoons disposed below each corner of theplatform 10. In this manner the level indicating means associated witheach corner of the platform will only be operative to close anelectrical circuit if the particular corner is displaced from a levelposition with respect to the center of the platform. For example, if theplatfrom 10 should tilt about the diagonal line through the center ofthe platform and the corners thereof above pontoons 23 and 25, the levelindicating means at 82 and 84 Will be tilted to close circuitstherethrough, while the level indicating means at 81 and 83 will not beso tilted as to complete a circuit. Similarly, if the platform 10 shouldtilt about the diagonal line extending through the center of theplatform and the corners thereof above pontoons 24 and 26, the levelindicating means at 81 and 83 will be operative to close electricalcircuits while the level indicating means at 82 and 84 will not betilted so as to close any circuit therethrough. If the platform istilted in any other direction, all of the level indicating means will beinclined to complete electrical circuits therethrough.

Again, the particular form of level indicating means need not be of theprecise form as that illustrated herein, as any similar means which willbe repsonsive to tilting motion of the platform 10 may be utilized, ifdesired.

In the operation of the device thus far described, a suitable site forexploratory drilling is selected and the anchor elements 33 are loweredinto position. Each anchor element is in the form of a rigid latticestructure and is relatively light and easy to maneuver into position.After the anchor elements are bottomed on the sea floor, rubble 86 isdumped onto the anchors to provide suflicient weight thereon to avoidany shifting of the anchor elements.

The platform is then towed into position, and the anchor cables 36-43,which have been held above Water by suitable means, are passed aroundthe pontoons and secured to the capstans 47 and 48 as previouslydescribed, with an approximately equal tension in each of the anchorcables.

The motor 50 is then actuated to take up on the anchor cables and topull the platform 10* downwardly so that the pontoons 23, 24, 25 and '26are submerged below the lowest sea level to be encountered, as from lowtides and/or wave action. The height of the bottom of the platform decksabove the pontoons is sufficiently great such that the platform deckswill always be above the highest sea level to be encountered, as fromhigh tides and/ or wave action. With the pontoon submerged to thedesired level, the brake arm 61 is fixed to gear shaft 56 to act as abrake for the capstan, and as a tension indicating device, as explainedpreviously. The capstan will not be again rotated until it is desired tomove the platform 10 to a new location.

Each pontoon 23-26 is designed to have a buoyancy force, when empty, ofapproximately 500 tons, and the total weight of the platform 10 andpontoons is approximately 800 tons. It is desired that the anchor cablesfurnish a downward force of 100 tons on each pontoon. In the drawings,the anchor cables are illustrated as extending at 45 angles from theanchor elements 33, although the precise angle is not critical and maybe more or less, as desired. In the case illustrated, for the anchorcables to produce a 100 ton downward force on each pontoon, each cablewill be tensioned to approximately 70.7 tons, or, the total cabletension of all eight cables will be approximately 565.6 tons. The springmember 66 of the tension responsive device 60 is set to this totaltension amount, and the generator 101 is connected into the controlcircuit of FIG. 7 by an appropriate switch.

If the pontoons are empty, or of such buoyancy that the total upwardforce exerted by the pontoons on the anchor cables is greater than theamount for which the tension responsive device 60 is set, the switchmember 68 will be moved into engagement with contact 102 of switch 69.This will complete a circuit from the low voltage secondary winding oftransformer 103 through each of the control relays 104, 105, 106 and107, to close the switches 108, 109,110 and 111, respectively, thusclosing the power circuits to the reversible motor-pump units 29, 30, 31and 32, causing each unit to pump Water into the pontoons 23, 24, 25 and26. When the total Weight of this water, or ballast, is such that thetotal cable tension is 565.6 tons, the switch arm 68 will be moved toits neutral, or off, position, opening the relay switches 109-112 todeactivate the pumps 29-32. Conversely, if the pontoons had had too muchballast therein, the switch arm 68 would have been in engagement withcontact 113, and relays 114, 115, 116 and 117 would have been energized,causing switches 118, 119, 120 and 121 to close, thereby energizing thepumps 29, 30, 31 and 32 to pump water out of the pontoons, thusincreasing the buoyancy of the pontoons until the total cable tension isincreased to the 565.6 ton amount. The interior of each pontoon isvented to atmosphere through a pipe 28, enabling a constant air pressureto be present in the pontoon at all times.

With the platform in its state of equilibrium as above described, eachpontoon will contain 200 tons of ballast, will be supporting 200 tons ofthe platform weight, and will be pulled downwardly by a force of 100tons by the two anchor cables acting thereon.

If any weight is added to the platform, as, for example, when a load ofsupplies is taken aboard, the total platform load will increase, and thetotal downward force due to the anchor cables will decrease. Thisdecrease of total cable force, or the tension therein, will cause theswitch arm 68 to engage contact '1 13, thereby energizing the pumps 29,30, 31 and 32 as above explained, to pump ballast out of each pontoonuntil the total cable tension is again at the desired amount.Conversely, if the total weight of the platform decreases, as, forexample, if the platform is unloaded, the total cable tension willincrease, causing switch arm 68 to engage contact 102, thereby causingthe pumps 29, 30, 31 and 32 to increase the ballast therein to decreasethe total cable tension to the desired amount.

With the apparatus thus described, the total weight of the platform andthe ballast in the pontoons is kept at a constant amount byautomatically varying the total amount of ballast inversely to the totalamount of platform weight. In this manner, it is possible to avoid thedisadvantages that would result from an excess of buoyancy, such asrequiring stronger anchor cable and greater horizontal stresses on thepontoons. Also, it is possible to avoid the disadvantage of having toolittle buoyancy, which would limit the amount of weight which could beadded to the platform. Further, by maintaining a constant tension on thecables, the amount of variation in elongation of the cables isminimized. As is apparent, the total weight of the platform and the loadthereon can be varied from no weight to 1600 tons without changing thetotal tension in the anchor cables.

In the foregoing discussion it has been assumed that the addition orsubtraction of weight to or from the platform has occurred on thevertical axis of the platform, so that the platform maintained a levelposition.

However, if the loading or unloading of the platform is eccentric, or ifa horizontal force is applied to the platform, the level responsivedevices at 81, 82, 83 and 84 will be actuated to maintain the platformat a level position, in a manner as will now be described.

FIG. 8 has been prepared to illustrate the manner in which the levelresponsive devices actuate the pumps when a horizontal force is applied,as from wind or tidal currents. The figure is simplified by consideringthe sidewards force to be applied on a line through the pontoons 23 and25, thus producing a tilting of the platform about a line throughpontoons 24 and 26. In such a case, the level responsive devices at 82and 84 will be inoperative and can be disregarded for purposes ofillustration. Furthermore, the anchor cables are illustrated as fixed tothe pontoons 23 and 25.

FIG. 8a thus schematically represents the pontoons 23 and 25, with therespective cables, at a point of normal equilibrium, and FIG. 8brep-resents the forces existing in the system at the normal equilibriumposition. Each pontoon 23 and 25 has an upward buoyant force of 100 tonsand a sidewards force (exerted on the platform structure) of 100 tonstending to pull the pontoons apart, and each set of cables A and B(representing cables 43, 36 and 39, 40) has a tension force of 141.4tons, the total tension in cables A and B being 282.8 tons.

FIG. illustrates a sidewards force of 40 tons as applied to the systemof FIG. 8a, for example as from a tidal current, and FIG. 8d illustratesthe forces on this system. The 40 ton sidewards force increases the tonsidewards force on pontoon 23 to tons, which produces an additional 28.3tons tension in cable A, and which produces a force of 28.3 tons,tending to move the pontoon 23 in a downward direction at right anglesto cable A, or tangentially to the arc of radius equal to the length ofcable A and with the anchor 33 as a center. At the same time, thesidewards force on pontoons 25 is decreased to 60 tons, which reducesthe cable tension in B by 28.3 tons, and which produces a force of 28.3tons, tending to move the pontoon 25 upwardly at right angles to cableB.

If the resultant forces of 28.3 tons tending to move pontoon 23downwardly and pontoon 25 upwardly are not compensated for, the systemwill move to a new position of equilibrium, as shown in FIG. 8e, withthe platform being tilted.

However, as soon as the platform begins to tilt, the level responsivedevices 81 and 83 will also be tilted so that they may act to compensatefor the side loading of the platform. The level responsive device 81will connect contacts 78 and 80 therein to establish a circuit throughrelay 105 and transformer 103, closing switch 109 to energize themotor-pump 29 to pump ballast out of pontoon 23. At the same time, thelevel responsive device 83 will connect contacts 79 and 80 therein, toenergize relay 116, closing switch 120 and actuating motorpump 31 topump ballast into pontoon 25. The pumps 29 and 31 Will continue tooperate until a sufiicient amount of ballast has been removed frompontoon 23 and a sufficient amount of ballast has been added to pontoon25 tocounteract the tide force of 40 tons. The forces existing on thesystem at this time are shown in FIG. 8 wherein an additional 40 tons ofbuoyancy acts directly upwardly on pontoon 23 (representing the decreasein ballast in pontoon 23) which in turn produces a 28.3 ton upward forceon pontoon 23 at right angles to cable A in balancing opposition to thedownward force therein produced by the 40 ton sidewards force. Also, anadditional 28.3 ton tension is produced in cable A. At the same time, anadditional 40 ton force is exerted on pontoon 25 directly downwardly(representing the increase in ballast in pontoon 25), which produces adownward force of 28.3 tons on pontoon 25 at right angles to cable B inequal opposition to the 28.3 ton upward force thereon exerted by the 40ton sidewards force. The cable tension in cable B is also lessened by28.3 tons.

FIG. 8g represents the system after the level responsive devices 81 and83 have compensated for the sidewards force, and FIG. 8h. represents theforces acting on the system. The total buoyant force acting upwardly onpontoon 23 is 140 tons, and the anchor cable A tension is 198 tons;while the total buoyant force acting upwardly on pontoon 25 is 60 tons,with the cable B having a tension of 84.8 tons. It will be noted thecombined vertical and horizontal forces acting on both pontoons 23 and25, produce resultant cable forces at 45 angles downwardly, so that theplatform is maintained at a level position.

It is to be noted that with a purely horizontal force applied, that thetotal cable tension in cables A and B remains at a constant value,although the individual tension in the diiferent cables may vary, andthus the tension responsive device 60 is not actuated to operate switch69.

If the sidewards force had been applied to the system in any otherdirection than that just described, the operation of the levelresponsive devices would be the same, except that in such a situationall four of the level responsive devices would be tilted, and wouldactuate the pumps associated therewith, so that if any one corner of theplatform were to tilt downwardly, the level responsive device at thatcorner would cause the pump in the pontoon at that corner to decreasethe ballast and increase the buoyancy of that pontoon to compensate forthe tilting. Similarly, if one corner of the platform tends to tiltupwardly, the buoyancy of the pontoon below that corner will bedecreased to compensate for the tilting.

In the discussion thus far, the platform has been subjected to eitherpurely vertical loads or purely horizontal loads. Any force applied tothe platform can be regarded as made up of vertical and horizontalcomponents, and the compensating systems thus described will compensatefor each of these components simultaneously with the cable tensionresponsive device 60 compensating for the vertical force component, andthe level responsive devices at 81, 82, 83 and 84 compensating for thehorizontal force component.

Returning to, FIGS. 7 and 8, let it be assumed that a downward verticalforce of lOOtons is applied at the same time that the 40 ton sidewardsforce is applied. From the previous discussion, it has been found thattons of ballast will be removed from the pontoons 23, 24, 25 and 26 tocompensate for an addition of 100 tons to the platform, and thus switcharm 68 will close against contact 113 to energize relays 114, 115, 116and 117 to actuate the pumps 29, 30, 31 and 32 to pump ballast out ofeach pontoon. However, as a result of the 40 ton horizontal forceapplied, the level responsive device 83 has been actuated to operaterelay 107 so that the pump 31 will pump the ballast into pontoon 25 tolevel the platform. To avoid having pump 31 attempting to both pumpballast into and out of pontoon 25 at the same time, an interlock relay126 is provided, to be energized by the closing of contacts 79 and 80 oflevel responsive device 83, so that when relay 126 is energized, it willopen switch 127 to interrupt the circuit from switch 69 to control relay107. In this manner, only a single of the control relays 107 and 116 canbe operated at any one time. After the platform has regained its levelposition, the relay 126 will be de-energized, allowing switch 127 toclose so that ballast may be pumped out of pontoon 25 to compensate forany vertical loading.

The pump 29 during this time has been energized by both the levelresponsive device 81 and the tension responsive device 60 to pumpballast out of pontoon 23. When the platform is level, the levelresponsive device contacts will open, but the pump will continue to pumpballast out of pontoon 23 until the tension responsive means issatisfied.

In a similar manner interlock relays 128, 1 29 and 130 have beenprovided so that if any of the level responsive devices 81, 82 or 84,respectively, signal that their respective pumps 29, 30 and 32 should beactuated to pump ballast into the pontoon, the tension responsive devicecannot signal the pumps to pump ballast out of the pontoons. Similarly,interlock relays 131, 132, 133 and 134 are provided so that if any ofthe level responsive devices 81, 82, 83 or 84, respectively signal thattheir respective pumps 29, 30, 31 and 32 should be actuated to pumpballast out of the pontoons, the tension responsive device cannot signalthe pumps to pump ballast into the pontoon.

In the control system thus described, the level responsive devices andtension responsive devices are each of a type wherein the devices givean off or on signal, with the level responsive devices overriding thetension responsive device in the control of the pumps in the pontoons.It is contemplated that other types of control systems may be used toaccomplish the same overall function as that described herein, as, forexample, the level responsive and tension responsive devices might be ofthe type wherein the magnitude of the change in level or tension ismeasured with suitable totalizing means being employed to summate themagnitude of the control signals in order to operate the ballast pumpsin the pontoons to provide for the proper correction of ballast in thepontoon in accordance with the varying loading conditions on theplatform.

In any event, if the buoyancy of the pontoons is controlled inaccordance with the preceding description, the platform will remain at afixed elevation above the floor of the sea and at a constant levelposition, even though the sea level may rise and fall due to tidalaction and wave action, and even though sidewards forces are applied tothe platform, as from wind, water currents, or eccentric loading of theplatform. Although FIG. 8 illustrates the platform as being canted aconsiderable amount from level with the addition of a sidewards force,it is to be realized that such canting as illustrated is merely for thepurpose of explanation. Under actual conditions of use, the sidewardsforces will be relatively small and the inertia of the relatively largeweight of the platform will prevent any sudden change in level position.It is desirable that the level responsive devices -8184 be sufficientlysensitive to indicate a slight change from level position, and thus theywill immediately start the ballast pumps into operation so that thepontoon buoyancies can compensate for the change in condition before theplatform is tilted to any significant amount.

If, at any time, before or after exploratory drilling, it is desired toerect a permanent, caisson supported, oil production platform, such aplatform is erected in the following manner. As illustrated, thepermanent platform 150 is comprised of four vertically extending hollowcaissons 151, 152, 153 and 154 connected together by conventionalstructural supports 156. The caisson structure is constructed insections, with an uppermost section being added to the structure, andthe whole platform 150 being then lowered in the water to provideworking room at the top thereof to add another section. This operationis repeated until the bottom of the platform 150 extends to the bottomof the sea.

Each caisson 151-454 is plugged at the bottom thereof so that theinterior of each caisson will be water-tight. In this manner, eachcaisson will be self buoyant so that the total weight on the platformwill not be varied as the caisson grows in length. The platformstructure 1511 is sunk in the sea by introducing ballast into thecaissons to overcome the buoyant force therein.

The axis of the permanent caisson structure .150 is maintained in avertical direction at all times by the aligning guides 157 mounted onthe platform which center the upper end of the caisson structure, and bythe caisson cables 161, 162, 163 and 164 acting on the bottom of thecaisson structure. As seen in FIGS. 2 and 4, cable 162 is bifurcated toform a yoke which is secured to caissons 151 and 152, the cable 162being passed around pulley 166 on anchor element 33 to extend upwardlyto winch 168 on platform 10. In a similar manner, cables 161, 163 and164 are yoked to the bottom ends of caisson 151-154 and are passedaround the anchor elements 33 upwardly to winches 167, 169 and "170,respectively. Each time the caisson structure 150' is lowered into thesea, the winches 167, 168, 169 and 170 are operated to take up an equalamount of cable, so as to center the axis of the caisson structure 150with the axis of the platform 10.

Since the top and bottom of the caisson structure is horizontally fixedrelative to the platform 10, the pontoons 23, 24, 25 and 26 Will serveto maintain the axis of the caisson structure in a vertical directionagainst any side forces thereon, as from underwater currents, in thesame manner as has been described.

After the caisson structure 150 has been bottomed on the sea floor,concrete is dumped around the bottom of the caisson units to provide apermanent footing. The platform anchor cables 36-43 are then fixed tothe upper end of the caisson structure 150, preferably under waterlevel, to provide lateral stability for the upper end of the caissonstructure. Since the platform anchor cables 3643 are passed around theinner sides of pontoons 23, 24, 25 and 26 in relatively close adjacencyto the caissons 151, 152, 153 and 154, the operation of transferring theanchor cables from the pontoons to the caisson structure may be easilycarried out.

The pontoons are then discharged of their ballast so that the platform'10 may be floated away from the permanent caisson structure 150 for thenext operation, and a permanent platform can be then built on the top ofthe caisson structure so that permanent drilling operations may becarried out. The hollow caisson will serve as well casings so thatdrilling operations may be 18 carried out therethrough without anypossibility or danger of contamination of the sea.

If desired, other forms of permanent caisson structures may be built,as, for example, a single large caisson may be erected.

If desired, the platform 16 may be constructed with auxiliary pontoons171 and 172 disposed beneath the upper platforms 11 and 12 in order toprovide a safety factor in the event that the buoyant force frompontoons 23, 2.4, 25 and 26 should be insufiicient at any time tosupport the weight of the platform.

In the discussion of the platform 10, a form thereof has beenillustrated in which four pontoons have been employed. However, theinvention is not intended to be restricted to a four pontoon system,since the same operation will result if a different number of pontoonsis employed. As, for example, the platform will operate in the samemanner if there are only three such pontoons, if the three pontoons arein a non-linear relationship, such that a verticalline extending throughthe centroid of the platform passes through the triangle defined by thepontoons. Similarly, the platform will operate in the same manner ifmore than four pontoons are employed. In each such arrangement, eachpontoon must have a level responsive device associated therewith andresponsive to the tilting of the platform in the vertical plane definedby such pontoon and the vertical axis of the platform, so as to be ableto operate the pump with-in that pontoon to adjust the buoyancy thereofto compensate for the tilting of the platform in that plane. Also, ineach such arrangement, a tension responsive device must be provided tobe responsive to the total anchor cable tension, regardless of thenumber of anchor cables employed.

It is to be understood that various changes in the shape, size andarrangement of parts may be resorted to Without departing from thespirit of my invention or the scope of the attached claims.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. A floating platform comprising a platform structure, a plurality ofbuoyancy tanks secured to and spaced beneath said platform, a pluralityof cables anchored at their lower ends and secured at their upper endsto the platform, said cables being tensioned with a suflicient totalforce to submerge the buoyancy tanks below their flotation level; meansresponsive to a change in total cable tension to adjust the buoyancy ofsaid buoyancy tanks to maintain the total tension in said cables withsaid sufiicient total force; and means responsive to a change from thelevel position of said platform for adjusting the buoyancy of saidbuoyancy tanks to maintain the platform in its level position.

2. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure; at least three anchor elements adapted to bedisposed on the bottom of the sea; a plurality of cable elements, eachhaving one end fixed to one of said anchor elements and the other endextending to said platform structure; means on said platform structureto produce a tension on said cables to submerge said buoyancy tanksbelow the surface of the sea; a reversible pump operatively associatedwith each of said buoyancy tanks operable to pump water in or out ofsaid buoyancy tanks to adjust the buoyancy thereof; means responsive tothe total cable tension in said cables; and means responsive to a changein the total cable tension to operate said pumps to change the buoyancyof said buoyancy tanks to correct for said change.

3. A floating platform of undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure; at least three anchor elements adapted to bedisposed on the bottom of the sea; a plurality of cable elements, eachhaving one end fixed to one of said anchor elements and the other endextending to said platform structure; means on said platform structureto produce a tension on said cables to submerge said buoyancy tanksbelow the surface of the sea; a reversible pump operatively associatedwith each of said buoyancy tanks operable to pump water in or out ofsaid buoyancy tanks to adjust the buoyancy thereof; means responsive tothe total cable tension in said cables; and means responsive to anincrease in total cable tension to operate said pumps to pump water intosaid buoyancy tanks and responsive to a decrease in total cable tensionto operate said pumps to pump water out of said buoyancy tanks, wherebysaid total cable tension is maintained at a desired amount.

4. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure, said buoyancy tanks being in a non-linearrelation; at least three anchor elements adapted to be disposed on thebottom of the sea in a non-linear relation; a plurality of cableelements, each having one end fixed to one of said anchor elements andthe other end extending to said platform structure; means on saidplatform structure to produce a tension on said cables to submerge saidbuoyancy tanks below the surface of the sea; a reversible pumpoperatively associated with each of said buoyancy tanks operable to pumpwater in or out of said buoyancy tanks to adjust the buoyancy thereof;means responsive to the total cable tension in said cables; meansresponsive to a change in the total cable tension to operate said pumpsto change the buoyancy of said buoyancy tanks to correct for saidchange; and means responsive to the tilting of said platform structurefrom a level position for operating said pumps to adjust the buoyancy ofsaid buoyancy tanks to bring the platform structure back to its levelposition.

5. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure, said buoyancy tanks being in a non-linearrelation; at least three anchor elements adapted to be disposed on thebottom of the sea in a non-linear relation; a plurality of cableelements, each having one end fixed to one of said anchor elements andthe other end extending to said platform structure; means on saidplatform structure to produce a tension on said cables to submerge saidbuoyancy tanks below the surface of the sea; a reversible pumpoperatively associated with each of said buoyancy tanks operable to pumpwater in or out of said buoyancy tanks to adjust the buoyancy thereof;means responsive to the total cable tension in said cables; meansresponsive to a change in the total cable tension to operate said pumpsto change the buoyancy of said buoyancy tanks to correct for saidchange; means responsive to a tilting of said platform structure; andmeans responsive to a change of the platform structure from its levelposition for operating said pumps to bring said platform structure backto its level position.

6. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure, said buoyancy tanks being in a non-linearrelation; at least three anchor elements adapted to 'be disposed on thebottom of the sea in a non-linear relation; a plurality of cableelements, each having one end fixed to one of said anchor elements andthe other end extending to said platform structure; means on saidplatform structure to produce a tension on said cables to submerge saidbuoyancy tanks below the surface of the sea; a reversible pumpoperatively associated with each of said buoyancy tanks operable to pumpwater in or out of said buoyancy tanks to adjust the buoyancy thereof;means responsive to the total cable tension in said cables; meansresponsive to an increase in total cable tension to 0perate said pump topump water into said buoyancy tanks and responsive to a decrease intotal cable tension to operate said pumps to pump water out of saidbuoyancy tanks, whereby said total cable tension is maintained at adesired amount; a plurality of level responsive devices, one eachassociated with an individual of said buoyancy tanks; and means operatedby a change from a level position by one of said level responsivedevices for operating the pump associated with the buoyancy tankassociated with said one level device to return said platform structureto its level position.

7. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure, said buoyancy tanks being in a non-linearrelation; at least three anchor elements adapted to be disposed on thebottom of the sea in a non-linear relation; a plurality of cableelements, each having one end fixed to one of said anchor elements andthe other end extending to said platform structure; means on saidplatform structure to produce a tension on said cables to submerge saidbuoyancy tanks below the surface of the sea; a reversible pumpoperatively associated with each of said buoyancy tanks operable to pumpwater in or out of said buoyancy tanks to adjust the buoyancy thereof;means responsive to the total cable tension in said cables; meansresponsive to an increase in total cable tension to operate said pump topump water into said buoyancy tanks and responsive to a decrease intotal cable tension to operate said pumps to pump water out of saidbuoyancy tanks, whereby said total cable tension is maintained at adesired amount; means responsive to a tilting of said platform structurein a vertical plane through each one of said buoyancy tanks and thecenter of said platform; and means actuated by said responsive means foractuating the pump associated with the buoyancy tank in said any oneplane to return the platform structure to level position in that plane.

8. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure, said buoyancy tanks being in a non-linearrelation; at least three anchor elements adapted to be disposed on thebottom of the sea in a non-linear relation; a plurality of cableelements, each having one end fixed to one of said anchor elements andthe other end extending to said platform structure; means on saidplatform structure to produce a tension on said cables to submerge saidbuoyancy tanks below the surface of the sea; a reversible pumpoperatively associated with each of said buoyancy tanks operable to pumpwater in or out of said buoyancy tanks to adjust the buoyancy thereof;means responsive to the total cable tension in said cables; meansresponsive to an increase in total cable tension to operate said pump topump water into said buoyancy tanks and responsive to a decrease intotal cable tension to operate said pumps to pump water out of saidbuoyancy tanks, whereby said total cable tension is maintained at adesired amount; means responsive to a tilting of said platform structurein a vertical plane through each one of said buoyancy tanks and thecenter of said platform; and means actuated by said tilting responsivemeans upon dipping of said platform structure from level in any one ofsaid planes for actuating the pump associated with the buoyancy tank insaid any one plane to pump water out of said buoyancy tank, and uponrising of said platform structure from level in said any one plane foractuating said pump to pump water into said buoyancy tank.

9. A floating platform for undersea operations comprising: a platformstructure; a plurality of buoyancy tanks secured to and spaced beneathsaid platform structure, said buoyancy tanks being in a non-linearrelation; at least three anchor elements adapted to be disposed on thebottom of the sea in a non-linear relation; a plurality of cableelements, each having one end fixed to one of said anchor elements andthe other end extending to said platform structure; means on saidplatform structure to produce a tension on said cables to submerge saidbuoyancy tanks below the surface of the sea; a reversible pumpoperatively associated with each of said buoyancy tanks operable to pumpWater in or out of said buoyancy tanks to adjust the buoyancy thereof;means to vent said buoyancy tanks to atmosphere; means responsive to thetotal cable tension in said cables; and means responsive to a change inthe total cable tension to operate said pump to change the buoyancy ofsaid buoyancy tanks to correct for said change.

References Cited in the file of this patent UNITED STATES PATENTSMinorsky Oct. 15, Voorhees Jan. 23, Crake Nov. 23, Armstrong May 7,Hansen Nov. 4, Lang July 19, Shrewsbury Apr. 11, Andresen July 3, Williset a1. Jan. 15, Stubbs Dec. 24, Parks June 9, Schurman et al June 7,

